1. Field of the Invention
The present description generally relates to power conversion.
2. Description of the Related Art
Distributed power systems (xe2x80x9cDPSxe2x80x9d) are employed in a large number of power generation applications. In particular, the use of small to medium size DPS in a variety of applications has risen in recent years. A DPS requires a low-voltage power supply (xe2x80x9cLVPSxe2x80x9d), typically In the range of 12 VDC to 24 VDC, for supplying power to a controller, gate drive, display control unit, customer interface unit, and other supporting units. The power rating of an LVPS typically ranges from a few hundred wafts to one kilowatt. The input of the LVPS is usually from the output of a DPS, which is typically in the range from 400-600 VRMS line-to-line.
The input voltage range of commercially available AC/DC converters is from 85 VRMS to 265 VRMS. Converters with input voltage range beyond 85-265 volts RMS, if even available, are very costly. An AC/DC converter of a few hundred watts having a 480 VRMS input costs between approximately $500 to $800. To make use of commercially available AC/DC converters with input voltage range of 85-265 VRMS, a step-down power transformer is required. The introduction of additional transformer adds extra costs, weight, size and many other negative factors to a DPS. Therefore, there is a need to design an AC/DC converter with wide input voltage range to cover all possible output voltages of a DPS.
The main concern in designing such an AC/DC converter is the high input DC voltage of the LVPS. For example, when the nominal output voltage of a DPS is 600 VRMS line-to-line, the line-to-neutral voltage is 347 VRMS. Considering that the output voltage of a DPS has a tolerance of xe2x88x9212% to +6%, the maximum line-to-neutral voltage will be 367 VRMS. After the input rectifier, the input DC voltage will be 519 VDC. The maximum voltage that the switching device in an AC/DC converter, such as a one switch flyback or forward converter, may be subjected to is up to 2.5 times the DC input voltage, i.e., the required voltage rating of a switching device may be as high as 1300 VDC. Most power MOSFETs that are commercially available are rated at 1200 VDC. With the consideration of the power rating and the input DC voltage of an LVPS, a two switch forward converter is desirable for this application. The maximum voltage that the switching device in a two switch forward converter may be subjected to is the same as the maximum input DC voltage. Thus, for example, the converter may employ 600 V power MOSFETS.
In one aspect, an electrical power converter includes a high voltage node, a low voltage node, a high frequency power transformer having a high voltage side and a low voltage side, the high frequency power transformer coupled between the high voltage node and the low voltage node, a controller operatively coupled to provide control signals to the high frequency power transformer, a controller power supply electrically coupled between the controller and the low voltage side of the high frequency power transformer to provide power to the controller from the low voltage side of the high frequency power transformer, and a startup circuit electrically coupled between the high voltage node and the high voltage side of the high frequency power transformer to provide control signals to the high frequency power transformer in response to power being applied to the high voltage node.
In another aspect, a circuit for an electrical power converter having a high voltage input and a low voltage output includes a high voltage bus having at least a first and a second high voltage rail, a low voltage bus having at least a first and a second low voltage rail, a transformer having a primary side and a secondary side, the primary side electrically coupled to respective ones of the first and second high voltage rails of the high voltage bus, the secondary side of the transformer electrically coupled to respective ones of the low voltage rails of the low voltage bus, the primary side having a number of power transistors, a startup circuit coupled to provide control signals in a first frequency range to the power transistors of the transformer in response to a voltage across the high voltage rails of the high voltage bus, a controller coupled to provide control signals in a second frequency range to the power transistors of the transformer, a controller power supply electrically coupled between the controller and the low voltage bus to provide a low voltage power to the controller during operation of the transformer, and a disable circuit electrically coupled to disable the control signals at the first frequency range while allowing the control signals at the second frequency range.
In another aspect, a converter having a high voltage node and a low voltage node includes transformer means for transforming a high voltage to a low voltage, startup circuit means for providing a first set of control signals at a first frequency to the transformer means in response to a high voltage at a high voltage node, and control means electrically coupled to a low voltage side of the transformer means for providing a second set of control signals at a second frequency, different from the first frequency, to the transformer means in response to a low voltage produced by the transformer means.
In a further aspect, a method of operating a converter having a startup circuit, a controller, and a high frequency power transformer having a high voltage side and a low voltage side includes providing a first set of control signals at a first frequency from the start up circuit to the high frequency power transformer in response to a high voltage supplied to the start up circuit, and providing a second set of control signals at a second frequency, different from the first frequency, from the control circuit to the high frequency power transformer in response to a low voltage supplied to the control circuit from the low voltage side of a high frequency power transformer.